Pipeline for offshore hydrocarbon production is installed on the seabed covering varying distances. Hydrocarbon well fluids carried by such pipeline can occur at high temperatures, e.g., greater than about 60° C., even up to about 200° C. Pipeline carrying such high temperature fluids experience thermal gradients across the pipeline during multiple shut downs and start ups resulting in expansion, contraction, and thermal cycling of the pipeline or conduit. This can result in a pipeline buckling in the lateral direction, displacement in the axial direction also referred to as “walking,” and loading that leads to both static peak and cyclic stresses, which may induce overstrain failure and fatigue failure along the length of the pipeline at locations vulnerable to these undesired failure mechanisms. Walking is a very costly problem, as the junction of the pipeline with elements of the production facility infrastructure, such as for example, a pipeline end termination (PLET) or other subsea equipment, can be overstressed, resulting in damage and even parting of the pipeline from the equipment. Such incidents often require that hydrocarbon production be shut down so that the pipeline system can be repaired.
In order to prevent undesirable pipeline movement in the lateral and axial directions, expensive anchoring mitigation using large suction driven piles and the like is often employed to hold the pipeline in place. Various techniques for controlling buckle initiation such as the use of sections of buoyancy modules installed on a section of pipeline have also been employed to control buckling of pipeline in the lateral direction Implementation of such mitigation solutions tend to be costly and complex. Additionally, in order to monitor pipeline movement, periodic surveys are conducted by remotely operated vehicles (ROV's).
Additional challenges are presented when subsea pipelines are routed through uneven terrain. For instance, a subsea pipeline may run across canyons and scarps. In such instances, free spans or sections of pipeline in which the pipeline is not supported by underlying seabed can be subject to externally imposed loads by surrounding currents and waves as well as internally imposed loads caused by flow instability, e.g., slug flow. These internal and external effects can cause vibrations and other movements in the pipeline that can result in pipeline overstress and fatigue failure. Furthermore, geographical hazards involving soil movement can overstress existing unsupported spans and/or create new ones.
It would be desirable to have an economical solution for controlling axial and lateral movements of subsea pipelines which would reduce the need for expensive pipeline anchoring or other mitigation solutions. It would additionally be desirable to have a convenient solution for monitoring the subsea pipeline. It would further be desirable to have a simple and economical solution to limit or control vibrations and movements in unsupported spans of pipelines routed through uneven terrain or subject to undesirable soil movement.